New trends in modern communication systems have emerged as a result of the growing data rate requirements for modern wireless systems and the need for multi-standard operation in smart wireless devices. The increasing demand of wireless services has made the radio spectrum a very scarce and precious resource. Most current wireless networks characterized by fixed spectrum assignment policies are inefficient, with only 15% to 85% of the licensed spectrum utilized on average.
To meet the high data rate requirements, reconfigurable MIMO antenna systems have gained in popularity over the past few years. This is because of their ability to operate according to the system requirements while keeping the MIMO functionality. A frequency reconfigurable antenna system can operate in MIMO configuration to enhance the system throughput and can support multiple wireless standards by switching its operation across different frequency bands. Thus, it helps to mitigate the spectrum congestion by efficiently utilizing the spectrum resources, which is the prime purpose of a CR platform.
CR is an adaptive, intelligent radio and network technology that can automatically detect available channels in a wireless spectrum and change transmission parameters enabling more communications to run concurrently and also improve radio operating behavior. The major advantage of a CR technique is its ability to utilize the idle or under-utilized spectrum resources. CR uses a number of technologies including Adaptive Radio (where the communications system monitors and modifies its own performance) and Software Defined Radio (SDR) where traditional hardware components including mixers, modulators and amplifies have been replaced with intelligent software.
Frequency reconfigurable MIMO antennas are the key front-end in a CR antenna system. Frequency agile MIMO slot antennas are suitable to be used as CR front-end antennas because of several advantages they offer. In addition to their capability to enhance system throughput, they are also easy to fabricate and are compatible with other microwave integrated circuits.
To enhance the capacity of a multiband or wideband communication system, it is necessary to implement reconfigurable characteristics in the system. These topologies are used to efficiently utilize the available frequency spectrum. The concept of CR is all about efficient frequency spectrum use. A CR based system has the ability to sense unoccupied frequency bands and has switching capability to change the operating point with increased data reliability and channel capacity. Moreover, MIMO technology is increasing in popularity because it provides high data rates with increased range and reliability. MIMO antennas are being utilized in 4G wireless standards.
Frequency agile antennas are an essential component of CR platforms. For efficient spectrum utilization, it is highly desirable to have antennas with wide-band operation or which can switch across several frequency bands. Reconfigurability is the fundamental requirement for CR applications in wireless devices. In addition, reconfigurable MIMO antenna systems are widely adopted in current communication systems to achieve the high data rate requirements within the available limited power and bandwidth channels. The key feature of a MIMO antenna system is its ability to multiply data throughput with enhanced data reliability, using the available bandwidth and hence resulting in improved spectral efficiency.
Exemplary prior includes the systems disclosed in issued U.S. Pat. No. 9,537,223 to Hall et al. and U.S. Pat. No. 8,957,817 to Jiang et al., and in published US patent application 2017/0062943 to Patron et al.
Hall et al. (U.S. Pat. No. 9,537,223) disclose a reconfigurable multi-output antenna (16) that comprises one or more radiating elements (12, 14), at least two matching circuits (42, 44, 50, 52) coupled to the or each radiating element (12, 14) via e.g. a splitter (30, 32) or a duplexer; and wherein each matching circuit (42, 44, 50, 52) is associated with a separate port (38, 40, 46, 48) arranged to drive a separate resonant frequency so that the or each radiating element (12, 14) is operable to provide multiple outputs simultaneously. Each matching circuit may be reconfigurable to enable their respective ports to tune their outputs to different frequencies. The matching circuits may comprise one or more than one inductor or capacitor (e.g. in the form of an L-C circuit) and may comprise a variable capacitor (i.e. varactor). (See figures and col. 10, lns. 47-col. 11, lns. 49).
Jiang et al. (U.S. Pat. No. 8,957,817) disclose a wireless communication system which is both miniaturized and reconfigurable. The antenna is a CPW (coplanar wave guide) square-ring slot antenna which is miniaturized and reconfigurable by the integration of ferroelectric (FE) BST varactors at the back edge of the inner conductor, or patch, of the antenna. The frequency of the antenna is reconfigurable due to the tunable capacitance of the FE varactors. (See figures and summary).
Patron et al. (2017/0062943) disclose a reconfigurable leaky-wave antenna that includes a plurality of cascaded metamaterial unit cells where each cell has a complementary resonator in its ground plane and adjustable varactor diodes that are biased to change a propagation constant through the plurality of cascaded metamaterial unit cells so that a directive beam from the antenna can be steered around an azimuth plane. (See figures and [0012]-[0014]).
To applicant's knowledge, no one has developed a compact, MIMO antenna for CR platforms for cellular communication front ends, wherein the antenna is frequency agile and has a wide tuning range covering several well-known wireless standards, including, among others, GSM1800, LTE, UMTS and WLAN.
Accordingly, there is need for a compact, MIMO antenna for CR platforms for cellular communication front ends, wherein the antenna is frequency agile and has a wide tuning range covering several well-known wireless standards, including, among others, GSM1800, LTE, UMTS and WLAN.